Screen Printing Printing Materials--Paper and Cardboard (1)

Part 2 Paper and Cardboard

The main raw materials for paper and board production are wood and water. The main components of the pulp are wood chip pulp, cellulose, waste paper and waste paperboard, which are about 95%. The remaining 5% are grass, straw and rags. About 50% of cellulose is contained in wood, and the rest is resin, lignin, protein and sugar. In spite of the variety of papers, they are made of wood. Classification of paper

There are many kinds of paper, and their respective characteristics are different. Some paper surfaces are smooth, some are rough; some have strong hygroscopicity, some do not absorb water; others are colored and white; opaque and transparent; lighter and heavier; Thin, but also thick; strong, but also soft.

The type of paper can be divided according to their use and the fiber content contained.

Divided according to use:
Printing Paper Packaging Paper Toilet Paper Various Cardboard Specialty Paper

According to fiber composition is divided into:

Wood fiber paper (newspaper, low-grade paper)
Chemical paper (writing paper, booklet and book paper)
Cloth fiber paper (manual paper analysis, paper for Henry, etc.)

Recycled paper is produced from waste paper. The writing paper should be suitable for writing with ink, so that the ink will not overflow on it. Therefore, it needs to be sizing, and the glue used has been added during the papermaking process. Printing paper should be resistant to ink or pigments and have a smooth surface; wrapping paper should be particularly strong; toilet paper such as napkins or toilet paper should have a strong hygroscopicity; cardboard should be bonded together by several layers of paper, weight is 150-600 g/m2; Boxboard is a heavy cardboard with a weight of 600 g/m2 or more. There are also specialty papers such as copy paper, greaseproof paper, label paper, poster printing paper, banknote paper and security paper. Identification of paper

In order to better process and print paper, screen printers must be able to identify the paper, must identify the front and back of the paper and vertical and horizontal, and can determine the moisture content of the paper. There are both simple and easy methods for identifying paper, as well as more expensive test instruments. Identifying the opposite side of the paper is relatively simple and rapid. The method is to approach the light source diagonally by hand, and the traces of the wire mesh in the paper can be seen. For glossy paper or coated paper it is more difficult. The following test method works well: cut two strips of paper in the transverse (width) of the paper, mark both sides of the two strips of paper and the base paper, immerse the strips in water together, and then you can see The paper roll is rolled up, and the outwardly convex side is the reverse side of the paper (ie, the stencil surface), and the concave side is the front surface of the paper, that is, the top surface. This is because the fiber expands laterally in water, which in turn lengthens the stencil surface (reverse surface). It is also easy to identify the fibre direction of the board, ie the feed direction. When a piece of rectangular cardboard is bent, the bending strength of the cardboard is greater in the fiber direction, that is, the feeding direction.

Another way to identify the direction of the cardboard fibers is to fold the cardboard between the tips of the fingers and the nails. If the creases appear a lot of undulations, fold them once again. If this crease is straight, then the direction of the fold is actually The fiber direction of the board is the feed direction. Waxed paper is not hygroscopic because its surface is closed and non-waxed paper absorbs water vapor quickly. The cleanliness of the paper, in a sense, is that there is no cloudy cloud on the paper, do not confuse it with transparency, this feature can be identified by observing the paper against the light source. Cloudy cloud spots arise from the beating process in the papermaking process, which is caused by poor material uniformity.

(to be continued)